<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <p id="test">hello world</p>
    <script>
        var test =document.getElementById("test");
        /* 
        nodeValue
        -->textNode,commentnode  会输出值，其他类型输出nu1ll
         */
        var txt =test.firstChild;
        console.log(test.nodeValue);
        console.log(txt.nodeValue);
        console.log(test instanceof Node);        
    </script>
</body>
</html>